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Suppose we have a list of boxes, here each entry has two values [start, end] (start < end). We can join two boxes if the end of one is equal to the start of another. We have to find the length of the longest chain of boxes.

So, if the input is like blocks = [ [4, 5], [5, 6], [4, 8], [1, 2], [2, 4] ], then the output will be 4, as we can form the chain: [1, 2], [2, 4], [4, 5], [5, 6]

To solve this, we will follow these steps:

if boxes are empty, then

return 0

sort the list boxes

dic := an empty map

for each start s and end e in boxes, do

dic[e] := maximum of dic[e] and dic[s] + 1

return maximum of the list of all values of dic

Let us see the following implementation to get better understanding:

import collections class Solution: def solve(self, boxes): if not boxes: return 0 boxes.sort() dic = collections.defaultdict(int) for s, e in boxes: dic[e] = max(dic[e], dic[s] + 1) return max(dic.values()) ob = Solution() boxes = [ [4, 5], [5, 6], [4, 8], [1, 2], [2, 4] ] print(ob.solve(boxes))

[[4, 5], [5, 6], [4, 8], [1, 2], [2, 4] ]

4

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